Neutrophil-mediated endothelial injury has been implicated in the pathogenesis of vascular damage in a variety of acute inflammatory disorders. This proposal considers two factors that modulate neutrophil-mediated endothelial injury. First, an activity in normal plasma that prevents oxidant-induced endothelial lysis in vitro is described and its characterization proposed. Since the luminal surface of vascular endothelium is bathed in plasma, inhibitory effects of normal plasma factor(s) on endothelial cytotoxicity in vitro are likely to be relevant to vascular injury by neutrophil-generated oxidants in vivo. Second, the role of stimulated neutrophil adherence to endothelium in the pathogenesis of endothelial damage is examined. Evidence suggests that close approximation of neutrophil and endothelial cell is necessary for cytotoxicity. Using in vitro and in vivo models, this proposal tests the hypothesis that inhibition of neutrophil adherence to endothelium prevents vascular injury in acute inflammation. The specific aims of this proposal are: 1) To isolate a factor(s) in normal human serum that inhibits lysis of cultured endothelial cells induced by exogenously-generated oxidants. This cytoprotective factor(s) will be isolated from serum by standard chromatographic techniques; 2) To determine the mechanism by which serum prevents oxidant-induced lysis of cultured endothelial cells. These studies will determine whether serum inhibits lysis of cultured endothelial cells induced by non-oxidant agents and whether serum inhibits sublethal (non-lytic) effects of oxidants on cultured endothelial cells; 3) To examine the role of neutrophil adherence in neutrophil-mediated endothelial injury in vitro. These studies will determine whether inhibition of stimulated neutrophil adherence by monoclonal antibodies (MoAbs) prevents sublethal endothelial injury and whether augmentation of neutrophil adherence by endothelial-dependent mechanisms promotes endothelial damage; 4) To determine whether a MoAb to a neutrophil membrane adhesion protein can inhibit neutrophil emigration in vivo. These studies will determine whether pretreatment of rabbits with a MoAb (60.3) that inhibits neutrophil adhesion in vitro prevents pulmonary sequestration and alveolar emigration of neutrophil induced by intravenous phorbol myristate acetate (PMA) or intrabronchial formyl-norleu-leu-phe (FNLP); 5) To determine whether inhibition of pulmonary sequestration and extravascular emigration of neutrophils by MoAb 60.3 prevents pulmonary edema induced by intravenous PMA or intrabronchial FNLP. These studies should provide insights into neutrophil-endothelial interactions in acute inflammation and perhaps suggest new therapeutic approaches to limiting vascular injury in inflammatory disorders.